Running the numbers on a cheap PSU

[Mike] picked up a cheap USB hub for four pounds (about $6) including delivery. He wanted to know how it’s possible to get quality electronics for that price, and as you may have guessed it’s not possible. He cracked open the power supply that shipped with the hub and hooked it up for some testing.

The wall wart has a sticker on it that claims a rating of 1 Amp at 5 volts. It’s pretty easy to see that this hardware cannot meet that spec just by looking at the circuit board. It’s a low-end single sided board that has some really disappointing isolation between the mains and regulated side of the circuit. As far as we can tell there’s really no reliable regulation circuit on the low side of the transformer, and the tests that [Mike] runs in the clip after the break show this. From left to right in the picture above you can see voltage at the hub-side of the power cord, current on the load, and voltage leaving the circuit board. At just 560 mA the voltage the USB hub is receiving has fallen below 3 volts!

Heh. I have a pair of those exact hubs, bought because they each contain a pair of Genesys GL850s. Obviously I don’t power them from the bundled PSU, but I might dig mine out and see what’s inside.

Regarding SMPS with only a single active component: you find that sort of thing in hardened stuff like warheads. They use exotic magnetic materials to achieve regulation over a reasonable load range. Not it this case though.

Found the hub PSUs and cracked one open. Mine’s pretty good – still no brand name but it has EMI filtering, a fuse, ok separation between output and input and optical feedback. Rated 5V, 2A and I paid £4.60 each with the hub, I just checked. I think you were ripped off Mike.

I just had a look at his second video where he does a walk through with a slightly better one. I thought that it actually makes for an interesting listen as to what makes designs better (strain relief, PCB material, creep gaps, filtering).

I’ll certainly never trust a cheap power supply again (not that I trusted them a great deal anyway).

I simply throw away all cheap chinese power supplies, these small ones are often extremely badly made.

Too bad i didn’t keep any of the worst ones, i had some really good examples a year ago. I was given a box of about 100 LiIon chargers, about 1 in 10 exploded when plugged in to the wall outlet, of the ones that didn’t explode about half actually worked.

It’s a 24V 4A power supply i bought on ebay for a project, the input is connected so that either hot or neutral is connected to ground, also the isolation distance between in and out is only 2mm. It doesn’t have an input filter either.

It’s really strange since the supply isn’t that bad otherways, it has a fuse, it can handle it’s full rated current and the soldering is well done. So except for being completely lethal and radiating interference it’s great!

The quality of cheap electronics probably depends more on your source than on them being cheap.
About a month ago I ordered 4 switching PSUs online. Two 12V 2A regular power adapters with Asian Power Devices Inc. on their labels and two 5V 3A supplies in a metal case with no brand label, but I can see pretty clean soldering and straight components through the holes.
€4.50 for each 12V and €6 for each 5V. These were ordered on a site where numerous consumers pay together to be able to get bulk discounts, so a lower price is justified and I’m fairly confident that these are fine.

My package with the components which I want to use the supplies for is being greatly delayed, however, so I haven’t been able to test them.
I’ll be sure to post about it if they do turn out to be complete garbage. And I would have to rethink my “Cheap is not always bad” stance.

It’s an interesting subject, anyone got any hints/tips on where to buy decent 5v/5.25v wall warts?

It’s also interesting to actually look at the hubs themselves, I was discussing this with a couple of guys the other day, turns out we’d all bought one of these hubs, all got slightly different designs, using the FE1.1 / 1.2 chips. One guy had a schottky seperating usb5v and DC in, mine had a resistor jumper (0ohm) where the diode should have been. They’re all hardwired as externally powered as far as your OS is concerned too.

Lots of missing caps, the holes were present, they just thought 1 was adequate.

Local electronic or hardware stores often have chargers that are reasonably well made to suit many different applications. Often they come with a two pronged connector on the end and an adapter to suit the various sized DC jacks on hardware. The ones from my local (old radio shack equivalent) store are all excellent and almost perfectly meet their stated output.

A good place to get decent adapters is old routers from some of the major brands like linksys. I have a linksys and a dlink adapter that are both siwtching designs and both can do 5V @ 2A very well, keeping regulation till the upper limit, they are also heavier than than the cheap counterparts.

Overall I tend to look for transformer based power supplies because even if it has a cheap output section the transformer is usually decent enough that I can salvage some use from it.Transformers also come with isolation by design, something switch mode supplies, especially cheap ones can lack.

A big thanks! I have a client who wants to source the absolute cheapest supplies he can for a product for which I am designing the controller. He is looking at $2 Chinese crap and this video and your previous story have helped me convince him of the error of his ways. I asked him how much liability insurance he wanted to carry.

Wow. I would have thought a switching power supply would have been regulated. Right from the start at 5.68 would stress most logic chips. The voltage should have stayed between 5.5v and 4.5v over the full current range. Imagine what that power supply would have done if it was regulated. zip boom. Been there done that.
Seeing this makes me wonder about some of the power supplies I have plugged in. Nothing as cheap as this but that does not mean much when it comes to oem sourced power supplies. On my personal projects I do tend to buy wall warts surplus but I do test them. On some projects I have used “enclosed” power supplies with exposed terminals for line and output. The only draw back is they need to be mounted in an enclosure due to the exposed terminal block. They work well, regulated with over load voltage fold back and over current shut down. Reading this post I am glad I went that route.

I like how all these ‘experts’ on the internet are oblivious to how engineering under a traded manufacturer works. Profit margin dictates more than most realize.. Management sources parts and moderates designs through secondary engineering stages..

It’s scary to think what state silicon manufacturing processes would be at if this was even half as true as I suggest.. for example.

A $1,000 Sandy Bridge i7 is only as good as what it’s microcode unlocks. Same with ARM IPs..same with analog designs and enclosure molding tech..

some textbook bob can tell me I’m wrong now cause they work at some firm or company nobody has ever heard of..

LOL
I just got one of those exact same hubs with power supply yesterday. I plugged in a single device and was concerned that on plugging in a second device that device worked then stopped working. I pulled out the meter and it was 4.5V no load and 3.6 with a load. Opened the adapter and it was pathetic just as the author stated. I can’t believe they can sell something like this, the solder joints were awful too.

If you have one of these hubs, you should open it up . If the soldering is anything like mine, you will have to re-do all the joints. I don’t know what kind of solder they used but I had to set my station to 475 degrees to melt it and then it was still a chunky mess ,even with added flux. There were also NO capacitors at all inside the unit, I had to add them to the places the board had provided for them .

Overall I spent more time making this cheap hub a decent hub than it was worth. Added 6 capacitors, a diode, and all new solder. Better to spend the extra cash and get decent quality. Oh well they were 2 for $10 .